While Robert Pattinson yukked it up with Jimmy Kimmel, the scorned woman in the Kristen Stewart-Rupert Sanders saga, Liberty Ross, hit the town for the Hollywood premiere of Lawless hosted by DeLeon Tequila Wednesday.

Looking serene and fresh-faced, the British model, 33, wore a silky green button-down shirt, skinny black pants, and black booties on her very first red carpet since her husband's affair -- but she declined to wear her wedding ring to the event, which she attended with her brother, Nine Inch Nails musician Atticus Ross.

After the screening of the film (starring Shia Labeouf and Guy Pearce) at the Arclight Theater, Ross headed to hotspot Eden for the DeLeon Tequila-hosted after party -- where she and her brother stayed lowkey, chatting with Australian rocker Nick Cave and other pals.

According to an observer, Ross -- whose surprise appearance was the buzz of the premiere -- spent most of the bash sipping on a drink and chatting quietly with her brother.

Together with Snow White and the Huntsman director Sanders, 41, for 15 years, Ross is mom to Skyla, 7, and Tennyson, 5. Ross learned of Sanders' July 17 fling with Stewart, 22, the week before Us Weekly's exclusive photos emerged. "She was coming to terms with it," a source told Us.